Color stabilized poly(arylene sulfide) resins

ABSTRACT

THE DISCOLORATION OF POLY(ARYLENE SULFIDE) RESINS IS MINIMIZED OR PREVENTED BY THE ADDITION OF A STABILIZING AMOUNT OF AN ORGANIC PHOSPHITE OR AN ORGANOPHOSPHINIC ACID. SPECIFICALLY, POLY(PHENYLENE SULFIDE) RESINS ARE COLOR STABILIZED BY THE ADDITION OF PHENYLPHOSPHINIC ACID OR DIOCTYLPHOSPHITE.

3,658,753 COLOR STABILIZED POLY(ARYLENE SULFIDE) RESINS Jerry 0. Reedand James S. Dix, Bartlesville, Okla, assignors to Phillips PetroleumCompany No Drawing. Filed July 1, 1970, Ser. No. 51,663 Int. Cl. C08g51/58 U.S. Cl. 260-45.7 P 8 Claims ABSTRACT OF THE DISCLOSURE Thediscoloration of poly(arylene sulfide) resins is minimized or preventedby the addition of a stabilizing amount of an organic phosphite or anorganophosphinic acid. Specifically, poly(phenylene sulfide) resins arecolor stabilized by the addition of phenylphosphinic acid ordioctylphosphite.

This invention relates to stabilized poly(arylene sulfide) resins. Inone aspect, it relates to poly(arylene sulfide) resins treated withorganophosphinic acids to inhibit discoloration. In another aspect, itrelates to poly (arylene sulfide) resins treated with organic phosphitesto inhibit discoloration. In another aspect, it relates topoly(phenylene sulfide) resins resistant to heat-induced discolorationby virtue of treatment with organophosphinic acids or organicphosphites.

BACKGROUND OF THE INVENTION Poly(arylene sulfides) which have not beensubjected to elevated temperatures, and which do not contain groupscapable of imparting color to the polymers are generally white or lightcolored. However, during high temperature curing, molding, or other heattreatment, the polymers often undergo considerable darkening. Thisdarkening occurs even though air is excluded during the high temperaturetreatment. For example, although poly- (p-phenylene sulfide) does notdiscolor when subjected to temperatures up to about 290 C. for one hourin a sealed, evacuated container, the polymer does become gray-brownwhen heated at 365 C. under the same conditions. Since it is frequentlydesirable to cure these polymers at temperatures as high as 425 C., thiscuring will result in an undesirable coloration of white or nearly whitepolymers. The term curing as used herein refers to heat treatment of thepolymers wherein the molecular weight of the polymer is thus increased.

Furthermore, even cured polymers, i.e., polymers whose molecular weighthas been increased by heating and which have been discolored thereby,which are subjected to later heat treatment for the purpose of moldingor coating, will undergo even further discoloration. This discolorationis aesthetically undesirable, and limits the application of these resinsin certain specific instances.

It is known to inhibit the discoloration of poly(arylene sulfide) resinsby the addition thereto of a monothiol or polythiol as disclosed in US.Pat. 3,386,950, issued June 4, 1968. It is also known that thediscoloration of poly- (arylene sulfide) resins can be inhibited by theaddition of a hydroxy-substituted amine as disclosed in US. Pat.3,408,342, issued Oct. 29, 1968.

In accordance with the invention, it has been found thatorganophosphinic acids or organic phosphites inhibit discoloration ofpoly(arylene sulfide) resins.

Accordingly, it is an object of this invention to provide a method oftreating poly(arylene sulfide) resins to reduce their discolorationtendencies.

It is a further object of this invention to provide a poly (arylenesulfide) resin composition with reduced tendency to discolor during heattreatment.

United States Patent O Patented Apr. 25, 1972 It is another object ofthis invention to provide a cured poly(arylene sulfide) resin of reduceddiscoloration.

It is yet another object of this invention to provide a stabilizedpoly(arylene sulfide) composition.

Other objects and aspects, as well as the several advantages of theinvention, will be apparent to those skilled in the art from theaccompanying disclosure and appended claims.

STATEMENT OF THE INVENTION In accordance with the invention,poly(arylene sulfide) resins are stabilized against discoloration bytreatment with at least one of an organophosphinic acid and an organicphosphite.

More specifically, according to the invention, poly- (phenylene sulfide)resins are treated by incorporating therein an organophosphinic acid oran. organic phosphite in an amount sufiicient to minimize or preventdiscoloration of the resin upon subjecting same to an elevatedtemperature such as normally employed during heat curing and/orfabrication steps.

Specifically, it has been found that phenylphosphinic acid ordioctylphosphite substantially minimizes discoloration of poly(phenylenesulfide) resins.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The term arylene sulfidepolymer as used in this specification is intended to include polymers ofthe type which are prepared as described in US. Pat. 3,354,129, issuedNov. 21, 1967, to Edmonds and Hill. As disclosed in this patent, thesepolymers can be prepared by reacting a polyhalo-substituted cycliccompound containing unsaturation between adjacent ring atoms and analkali metal sulfide in a polar organic compound. The resulting polymercontains the cyclic structure of the polyhalosubstituted compoundcoupled in repeating units through a sulfur atom. The polymers which arepreferred for use in this invention, because of their high thermalstability and availability of thematerials from which they are prepared,are those polymers having the repeating unit -R4 where R is phenylene,biphenylene, naphthylene, biphenylene ether or a lower alkyl-substitutedderivative thereof. By lower alkyl is meant alkyl groups having 1 to 6carbon atoms such as methyl, propyl, isobutyl, n-hexyl, and the like.The preparation of such polymers is quite well disclosed in the abovepatent of Edmonds et al.

The polymers of this invention are preferably those which have meltingtemperatures above about 204 C. These arylene sulfide polymers can havea melting temperature anywhere in the range from 204 C. to 482 C.Polymers of phenylene sulfide normally have melting temperatures in therange from about 288 to 482 C. The preferred polymers have an inherentviscosity in chloronaphthalene at 206 C. of at least 0.1, morepreferably between 0.1 and 0.3 and ideally between 0.13 and 0.23.

The invention is broadly applicable to polyarylene sulfides formed byany technique. It can be used, for example, with the resins manufacturedas described in US. Pat. 2,513,188 prepared by reacting mixtures ofp-dichlorobenzene and 1,2,4-trichlorobenzene with sulfur and a metalhalide at fusion temperatures. It can also be used with resinsmanufactured by the method described in British Pat. 962,941 whereinmetal salts of halothiophenols are heated at a polymerizing temperature.The invention is especially useful with polymers produced by reactinganhydrous sodium sulfides with polyhalo-substituted cyclic compounds inpolar organic solvents as disclosed in US. 3,354,129. The invention canbe used with linear polymers formed by use of dihalo aromatic compoundsor with crosslinked polymers wherein polyhalo aromatic compounds areadded to the polymer to aid crosslinking.

The organophosphinic acids that can be employed according to theinvention can be represented by the formula it) HO P wherein R is eitherhydrogen or an aryl group with at least one R being an aryl group. Thearyl group can be monocyclic or polycyclic, preferably an aryl group containing no more than three rings. The R group includes such radicals asphenyl, tolyl, ethylphenyl, butylphenyl, propyltolyl, ethylhexylphenyl,naphthyl, anthryl, phenanthryl, and the like.

Representative examples of organophosphinic acid that can be employedinclude phenylphosphinic acid, diphenylphosphinic acid,phenyl(l-naphthyl)phosphinic acid, 8- anthrylphosphinic acid,di(3-phenanthryl)phosphinic acid, 4-eicosylphenylphosphinic acid,di(2,4,6-triethylphenyl)- phosphinic acid, and the like.

The amounts of the organophosphinic acids utilized in the polyphenylenesulfide can vary from about 0.01 to about 20.0 parts by weight per 100parts of the polymer. A more preferred range is from about 0.25 to about3.0 parts acid per 100 parts polymer.

The organic phosphites that can be employed according to the inventioncan be represented by the formula wherein R is a hydrocarbon groupselected from alkyl, aryl, cycloalkyl, alkaryl, and aralkyl groupshaving from 1 to carbon atoms, and R" and R' are selected from R andhydrogen.

Typical examples of such phosphites include isobutyl phosphite, ethylphosphite, cyclohexyl phosphite, phenyl phosphite, tridecyl phosphite,eicosyl phosphite, l-naphthyl phosphite, Z-phenanthryl phosphite,1-(3,5,7-triethylanthrycyl) phosphite, di(2-phenylethyl) phosphite,di(hexadecyl) phosphite, dicyclopentyl phosphite, dioctyl phosphite,diethyl phosphite, di(tridecyl) phosphite, dibutyl phosphite, diphenylphosphite, didecyl phosphite, cyclohexyldecylphenyl phosphite, trioctylphosphite, trimethyl phosphite, triethyl phosphite, tributyl phosphite,triisobutyl phosphite, tri(sec-butyl) phosphite, tri(tert-butyl)phosphite, trihexyl phosphite, tricyclohexyl phosphite, tri-(2-ethylhexyl) phosphite, triisooctyl phosphite, tri(tridecyl)phosphite, tri(heptadecyl) phosphite, tri(octadecyl) phosphite,trieicosyl phosphite, phenyldidecyl phosphite, phenyldi(hexadecyl)phosphite, phenyldi(nonadecyl) phosphite, diphenyldecyl phosphite,diphenylheptadecyl phosphite, diphenylnonadecyl phosphite, triphenylphosphite, tri(p-octylphenyl) phosphite, tri(l-naphthyl) phosphite,tri(Z-naphthyl) phosphite, tri(p-dodecylphenyl) phosphite, and the like,e.g., tri(nonylphenyl) phosphite.

Particularly suitable phosphites are dior trioctyl phosphite, diethylphosphite, dibutyl phosphite, diphenyl phosphite, and dior tridecylphosphite. Of these, dioctyl phosphite is presently preferred.

The amounts of the organic phosphites utilized in the poly(arylenesulfide) resin can vary from about 0.01 to about 20 parts by weight per100 parts of the polymer. A more preferred range is from 0.25 to about 3parts organic phosphite per 100 parts polymer.

The organophosphinic acid or organic phosphite can be incorporated inthe polymer prior to heat treatment in any convenient manner. Forexample, the organophosphinic acid or organic phosphite can be added assuch to the polymer and the resulting mixture can be agitated in anysuitable manner to achieve good mixing.

The stabilizing acid can he added to the polymer in several ways. Forexample, the acid can be dissolved in a suitable solvent such asacetone, methanol-water, etc. The solution is sprayed on the polymer orslurried with the polymer to distribute the additive. If desired, thetreated polymer is given additional mixing in a tumble blender, Henschelmixer, etc., to more thoroughly distribute the additive. The mixingdevices mentioned can also be used to blend the powdered acid with thepolymer powdenlt is also feasible to incorporate the stabilizer inmolten resin by using a Banbury mixer, Brabender mixer, extruder, andthe like.

It is also within the scope of the invention to admix the polymer andcolor stabilizing phosphorus compound with suitable plasticizing agents,dyes, fillers, pigments, and the like.

Heat treatment of the polymer and color stabilization or reduction withthe phosphorus compounds of the invention can be accomplished byincorporating the phosphorus additive into the polymer and thensubjecting the polymer-containing additive to a curing temperature suchas an elevated temperature in the range -400" 0., preferably about200370 C., for a period of about one hour to about 24 hours, preferablyabout three hours to about twelve hours.

The compositions of the invention can be used as coatings on varioussubstrates such as metals and ceramics. The compositions are suitablefor preparing many useful articles by injection molding, extrusion andcompression molding techniques. Such articles include profiles,mechanical parts, containers and the like.

SPECIFIC EXAMPLE Color stabilizing additives of the invention were meltblended (one percent by weight) with polyphenylene sulfide for tenminutes under a nitrogen blanket in a Brabender mixer at a temperatureof about 290 C. The control was similarly treated. A film, 5 mils thick,was compression molded from each of the samples at about 330 C. under apressure of 30,000 p.s.i.g. for 30 minutes and then cooled rapidly. Thecolor of each film was visually evaluated according to the Gray ScaleFor Staining Test devised by the American Association of TextileChemists and Colorists (AATCC). In this test a gray color is comparedwith a white standard. A rating of 1 indicates that a sample has changedin color from white to about black. A rating of 5 indicates no changefrom the white standard. The results are presented in Table I.

TABLE I Additive used: Gray scale rating None (control) 1.5Phenylphosphinic acid 3.5 Dioctyl phosphite 2.0

These data show that the color of polyphenylene sulfide resin subjectedto elevated temperatures during melting and molding are reduced byincorporating such additives into the resin prior to the heat treatment.The formulations of Table I containing the additives are suitable forcoating applications and the like.

We claim:

1. A color stable composition comprising a polyarylene sulfide resin anda stabilizing amount of at least one phosphorus-containing compoundselected from (a) organophosphinic acid as represented by the formula H/HOP wherein R is selected from hydrogen and aryl groups with at leastone R group being an aryl group, and

(b) organic acid phosgiites represented by the formula RO-P wherein R'is a hydrocarbon group having one to 20 carbons and R and R' areselected from R and hydrogen.

2. A composition according to claim 1 wherein the amount ofphosphorus-containing compound present in the resin is in the range 0.01to 20 parts by weight per 100 parts of the resin.

3. A composition acording to claim 1 wherein the resin is apoly(phenylene sulfide) resin and the phosphorus-containing compound isphenylphosphinic acid.

4. A composition according to claim 1 wherein the resin is apo1y(phenylene sulfide) resin and the phosphorus-containing compound isdioctyl phosphite.

5. A heat cured product resulting from the color stable composition ofclaim 1.

6. A molded product formed from the color stable composition of claim 1.

7. A heat cured product according to claim 5 wherein the resin ispoly(phenylene sulfide) and the phosphoruscontaining compound isphenylphosphinic acid or dioctyl phosphite.

8. A molded product according to claim 6 wherein the resin ispoly(pheny1ene sulfide) and the phosphorus-containing compound isphenylphosphinic acid or dioctyl phosphite.

References Cited UNITED STATES PATENTS 3,509,091 4/1970 Cleveland et al.26045.8 2,553,643 5/1951 Ellerhorst, Jr. 260-457 2,564,646 8/1951Leistner et a1. 26045.7 2,733,226 1/1956 Hunter 26029.7 3,305,520 2/1967Fritz et a1. 26045.7 3,373,146 3/1968 Meyer et al 260--79.7 3,429,8502/1969 Holoch 260-459 3,449,292 6/1969 Snedeker 26045.7 3,489,702 1/1970 Abramolf 260-18 3,493,538 2/1970 Salyer et al. 26045.95

DONALD E. OZAJA, Primary Examiner R. A. WHITE, Assistant Examiner US.Cl. X.R. 26079

